DE102017122921A1 - Method for producing a Planetenradbolzens with increased hardness - Google Patents

Abstract

A method of hardening a planetary gear bolt includes carbonitriding an outer peripheral surface of the planetary gear bolt and quenching the planetary gear bolt in oil at a temperature of between about 120 ° and 150 ° C. The method also includes quenching the planetary gear bolt in a fluid at a temperature of between about - 70 and -120 ° C and starting the Planetenradbolzens. After tempering, the outer peripheral surface of the planetary gear has a surface hardness of HV 832 or more, with the bolt material maintaining a hardness of at least HV 513 to a depth of at least 0.5 mm. It is also possible to perform additional steps such as high temperature annealing and induction hardening to realize soft ends on the bolt for caulking.

Description

Field of the invention

The present disclosure relates to a method of manufacturing a planetary gear bolt, and more particularly to a method of manufacturing a planetary gear bolt of increased hardness.

background

Planetary gears and planetary gear sets are used in various types of applications including vehicle systems. An example of a planet gear is a pinion gear rotatably mounted on a pin by a radial bearing. The bolt is connected on both sides with a carrier, which may also have additional pinion gears. In some applications, planetary pins are subject to high surface contact pressures and high temperatures. Increasing demand for smaller planetary gear sets and planetary gear components or higher torque inputs in vehicle applications has resulted in higher power density and higher surface contact pressures on planetary pin bolts.

Such planetary pin could require sufficient hardness and mechanical strength to withstand surface contact pressures of 5000 MPa or more and at the same time maintain sufficient fatigue life under rolling contact and dimensional stability at elevated temperatures. These properties are difficult to achieve with low cost materials and processes.

In particular, currently common heat treatment processes for hardening Planetenradbolzen in the case of smaller bolts can not produce the necessary hardness. Alternative options for achieving localized surface hardness, such as shot blasting, plating, coating, etc., do not produce sufficient surface hardness and / or depth of cure and may not provide quality raceway surfaces on radial bearings. Furthermore, materials that inherently possess the necessary properties are not economically viable. Accordingly, there exists a need for a method of tempering low cost materials (e.g., steel alloys) which are suitable for the manufacture of planet gear bolts having sufficient hardness properties to withstand increased surface contact pressures acting on the bolts.

The object of the present disclosure is to propose ways of overcoming these and other problems existing in the prior art.

Summary

According to one embodiment, the present disclosure relates to a method of hardening a planetary pin. The method includes carbonitriding an outer peripheral surface of the planetary pin and quenching the planetary pin in oil at a temperature between about 120 and 150 ° C. The method also includes cryogenic quenching the planetary pin in a cryogenic liquid at a temperature between about -70 and -120 ° C, and starting the planetary gear bolt. After tempering, the outer peripheral surface of the planetary gear has a surface hardness of HV 832 or more, with the bolt material maintaining a hardness of at least HV 513 to a depth of at least 0.5 mm.

According to another embodiment, the present disclosure relates to a method of manufacturing a planetary gear set. The method includes hardening a planetary gear bolt by carbonitriding an outer peripheral surface of the planetary gear pin and quenching the planetary gear pin in oil at a temperature between about 120 and 150 ° C. The method also includes cryogenic quenching of the planetary gear bolt in a cryogenic liquid at a temperature between about -70 and about -120 ° C, and starting the planetary pin. After tempering, the outer peripheral surface of the planetary gear has a surface hardness of HV 832 or more, with the bolt material maintaining a hardness of at least HV 513 to a depth of at least 0.5 mm. The method also includes attaching a roller bearing radial bearing unit and a gear toothed wheel body to a planetary pin, and attaching opposite ends of the pinion pin to a carrier.

In some embodiments, the hardening includes high temperature tempering of the planetary pin and induction hardening of the surface of the pinion pin after quenching in oil and quenching in the cryogenic liquid. In a method involving these additional steps, end faces of the planetary pin have a hardness of between HV 170 and HV 350.

In still other embodiments, in addition to tempering after quenching in the cryogenic liquid, tempering includes tempering the planetary pin after quenching in oil and before high temperature annealing.

list of figures

• 1 eine Querschnittsansicht eines Abschnittes eines Planetenradsatzes,
• 2 eine Darstellung eines Bolzens, der in Zusammenhang mit dem Planetenradsatz gemäß 1 verwendet werden kann,
• 3 ein Ablaufdiagramm eines beispielhaften Härtungsverfahrens für die Behandlung eines Bolzens,
• 3A eine Darstellung eines Bolzens nach einem Karbonitrierungs-Schritts, und
• 4 ein Ablaufdiagramm eines anderen beispielhaften Härtungsverfahrens für die Behandlung eines Bolzens, einschließlich der Schritte für die Herstellung von weicheren Enden für das Verstemmen.

The foregoing summary and the following detailed description will be better understood when read with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. The figures show:

• 1 a cross-sectional view of a portion of a planetary gear set,
• 2 an illustration of a bolt, in connection with the planetary gear according to 1 can be used,
• 3 FIG. 3 is a flowchart of an exemplary curing process for the treatment of a bolt. FIG.
• 3A a representation of a bolt after a carbonitriding step, and
• 4 FIG. 5 is a flow chart of another exemplary curing process for the treatment of a bolt, including the steps for making softer ends for caulking. FIG.

Detailed description of the preferred embodiments

In 1 is a section of an exemplary planetary gear set 10 shown. The planetary gear set 10 has a carrier 12 and a planetary gear 14 on. Although only one planetary gear 14 is shown, it is understood that the carrier 12 also additional planet gears 14 can have. For example, the planetary gear 14 a pinion gear of a plurality of planetary gears, which in a star shape around an axial center of the carrier 12 are arranged.

In an exemplary embodiment, the planet gear 14 a wheel body 16 on, a plurality of wheel teeth 18 and a storage unit 20 and a bolt 22 , The wheel body 16 has a substantially cylindrical shape and has a central bore for receiving the bearing unit 20 on. The storage unit 20 is one with roles 24 provided radial bearing. The roles 24 preferably have a cylindrical shape, but may also have other shapes. The roles 24 can also be stored in a warehouse 26 be held and positioned.

The roles 24 are formed so that they can roll between two opposing raceways. For example, a first raceway may be through an inner surface of the wheel body 16 or by a separate component of the storage unit 20 be formed. A second career is preferably by the bolt 22 educated. In other words, the roles 24 in contact with and rolling on an outer surface 28 of the bolt 22 ,

During operation comes the planetary gear 14 in engagement with other transmission components (eg, a sun gear and / or a ring gear), whereby a driving force on the planet gear 14 is applied. The driving force includes a surface contact pressure acting on the bolt 22 is transmitted. In some cases, this surface contact pressure may be 5000 MPa or more. Coupled with the high operating temperatures that could prevail, the bolt can 22 be prone to deformation. For this reason, the bolt needs 22 Possess features that can resist these conditions, so the planetary gear 14 remains operational for a desired life of its parts.

In 2 is still the bolt 22 shown. The bolt 22 has a middle section 30 and a pair of opposite end portions 32 on. The outer surface 28 of the bolt 22 extends through the middle section 30 and through between the opposite end faces 34 lying end portions 32 , The end surfaces 34 are circular surfaces that are substantially perpendicular to the outer surface 28 and extend parallel to each other. Essentially, the middle section corresponds 30 the section of the outer surface 28 who is in contact with the roles 24 stands. In other words, the length of the middle section 30 about as long as a length of rolls 24 , The end sections 32 are each between the middle section 30 and a respective end surface 34 limited.

It must be at least the middle section 30 have sufficient hardness to provide a stable running surface for the rollers 24 which is capable of withstanding a high surface contact pressure at high temperatures. In an exemplary embodiment, it has been determined that this sufficient hardness must be at least HV 832. Furthermore, to form a stable tread, this hardness must be deep enough from the outer surface 28 in the body of the bolt 22 extend into it. In particular, this hardness needs a depth 36 of hardened material to be sufficient. In at least some implementations it has been determined that the depth of hardened material at which the hardness does not fall below HV 513 should be at least 0.5 mm. This surface area is on a hardened section 40 identified. Although this hardened section 40 only near the surface of the bolt 22 is shown, it is understood that the depth of the hardened portion of the size of the radius of the bolt 22 can be, so the size of the hardened section 40 of the bolt 22 up to the size of the entire body of the bolt 22 can own. The depth of the hardened section 40 depends on several factors including the material of the bolt 22 and the parameter of the curing process.

The way of fastening bolt 22 to the carrier 12 will also affect the mechanical properties of the bolt 22 exercise. For example, in some designs the bolt is 22 preferably by a Stemmverfahren to the carrier 12 attached. As in 1 As shown, a caulking method involves deformation of a portion 38 the end surfaces 34 of the bolt 22 to make a press fit between the bolt 22 and the carrier 12 to create. Around the ends of the bolt 22 However, the hardness of the end sections must be caulked 32 and in particular the end surfaces 34 less than HV 832, but which hardness for the outer surface 28 in the middle section 30 necessary is. Preferably, for example, the end surfaces 34 a hardness of between HV 170 and HV 350. It should be understood that other methods for fastening the bolt 22 to the carrier 12 can be used. In these other methods (eg screwed or glued joints etc.) it is not necessary that the end sections 34 are softer.

The invention discloses a curing method to achieve the above-described mechanical properties in the bolt 22 obtained from an economically suitable material such as a steel alloy. The hardening process will vary, depending on the way the bolt is used 22 to the carrier 12 should be attached. For example, in the case where the bolt 22 in the carrier 12 caulking, the curing process will have additional steps to the softer end portions 32 to produce.

In 3 is an exemplary curing process 300 for the treatment of the stud 22 shown. The curing process 300 involves carbonitriding the bolt 22 (Step 310). For example, an outer peripheral surface becomes 28 of the bolt 22 exposed to a gas mixture that causes carbon atoms and / or nitrogen atoms in the bolt 22 diffuse into it.

In 3A is the bolt 22 after the carbonitriding step. In particular, an enriched area 42 formed (extending from the outer peripheral surface 28 to a selected depth) containing a high concentration of carbon atoms and nitrogen atoms which produce properties that increase hardness after quenching in oil and allow further curing.

After carbonitriding the bolt becomes 22 quenched in an oil bath (step 320). For example, the bolt will 22 quenched in oil at about 120-150 ° C. As a result of quenching in oil gets the enriched area 42 a surface hardness of about HV 800-940. The depth of the increased surface hardness depends on the base material of the bolt 22 from.

For example, if the bolt 22 made of a low-carbon steel, the hardened section is limited 40 usually on an area near the surfaces of the bolt 22 , as in 2 shown. Is the bolt 22 made of a high-carbon steel, becomes the hardened section 40 through the entire body of the bolt 22 expand (eg, it will not be much smaller at any depth), such that the depth of the hardened section 40 the same size as the radius of the bolt 22 ,

Quenching in oil turns austenite into martensite, increasing the hardness in the hardened section 40 arises. However, it is possible that the amount of residual austenite (eg, austenite that was not transformed into martensite) after quenching in oil is still relatively large. For example, the remaining austenite may be about 5 to 25% of the material in the cured section 40 of the bolt 22 turn off. In versions made of hard steel, in which the bolt 22 after quenching in oil can be through hardened, the amount of remaining austenite of between 5 and 25% could only for the enriched section 42 corresponding area apply.

To the bolt 22 To further harden, the bolt becomes 22 then treated with cryogenic quenching (step 330). For example, the bolt will 22 immersed in a cryogenic liquid (eg, in liquid nitrogen) at a temperature of between about -70 and -120 ° C. The cryogenic quenching process further transforms the austenite (eg, remaining austenite after quenching in oil) into martensite, causing the plug 22 is further hardened. For example, the amount of remaining austenite is in the cured section 40 less than 5% after cryogenic quenching. This may, depending on the bolt 22 used material, for the entire enriched section 40 or only for the enriched section 42 corresponding area apply.

Thereafter, the low-temperature quenched bolt 22 started (step 340). The tempering treatment helps to create residual stresses in the bolt 22 reduce stretchability and reduce brittleness. For example, brittle tetragonal martensite is transformed into more ductile cubic martensite. In one execution The tempering treatment involves exposing the bolt 22 a temperature of about 180-230 ° C, followed by air cooling at ambient temperature.

After the tempering step, it is at least the outer peripheral surface of the bolt 22 holding the hardened section 40 having a hardness of at least HV 832 and a hardened material depth of at least 0.5 mm, in which the hardness does not fall below HV 513. As a result of method step 300, the end faces 34 have a similar hardness as the outer peripheral surface 28 , As a result, through the method 300, hardened planetary pins can be made by a method other than caulking or otherwise deforming the bolt 22 to the carrier 12 be attached. As further described below, softer end sections can be used 32 To obtain additional treatment steps are performed.

In 4 is another curing process 400 for the treatment of the bolt 22 shown. The curing process 400 includes steps, the softer end portions 32 produce, and thereby caulking the bolt 22 in the carrier 12 enable. The curing process 400 includes carbonitriding (step 410) and quenching in oil (step 420) similar to that described in process 300. At this point, an optional annealing step (step 425) may be performed.

After quenching in oil (or optional tempering) the bolt becomes 22 tempered at high temperature (step 430) to achieve the required low hardness in the end sections 32 to obtain. The high temperature tempering step may involve heating the bolt 22 to about 650 ° C or higher for a period of 2-4 hours followed by slow cooling back to ambient temperature. The high temperature tempering step reduces the hardness of the bolt 22 for example to approx. HV 170-350. In this condition, the microstructure is ready for post curing and the ends of the bolt 22 are soft enough to allow caulking to be performed. The step of high temperature tempering may alternatively be considered as annealing.

Next is the bolt 22 induction hardened (step 440). The step of induction hardening is applied only to the middle section 30 of the bolt 22 performed to the raceway sections of the bolt 22 to harden (ie not on the end surfaces 34 ). This is realized by induction hardening the outer surface 28 followed by quenching. In an exemplary embodiment, the induction hardening step includes heating at a temperature of 800-1050 ° C followed by quenching in oil.

After performing the quench associated with the induction hardening step, the hardened portion contains 40 about 5-25% remaining austenite and a hardness of about HV 700-900. On the other hand, the end surfaces are not significantly affected by the induction hardening step, and maintain a softer, workable structure.

Around the outer surface 28 Further, method 400 further involves low temperature quenching of the stud 22 (Step 450) and cranking (step 460). These steps may be identical to steps 330 and 340 of method 300 described above. For example, the induction hardened bolt 22 immersed in a cryogenic liquid (eg, in liquid nitrogen) at a temperature of between about -70 ° and -120 ° C. The low temperature quenching further converts austenite (eg, austenite remaining in oil after quenching) to martensite, which is the stud 22 continues to harden. After cryogenic quenching, the proportion of residual austenite in the cured section is 40 less than 5%. The tempering step reduces the residual stresses and improves the ductility.

After the tempering step, the outer circumferential surface of the bolt 22 the hardened section 40 , which has a hardness of at least HV 832 and an effective case hardening depth 36 of at least 0.5 mm with HV 513. As a result of method 400, the end surfaces remain 34 soft and have a hardness of between HV 170 and HV 350. Thus, hardened by the method 400 planetary pin by caulking to the carrier 12 be fastened, in which the ends are deformed to the bolt 22 to the carrier 12 to fix.

The exemplified methods 300 and 400 form alternative methods for hardening a planetary gear bolt such that an outer peripheral surface of the planet gear pin has a hardened portion having a surface hardness of HV 832 or more, the bolt material having a hardness of at least HV 513 to a depth of at least 0.5 mm. The methods involve several common steps, including cryogenic quenching, which eventually leads to high hardness characteristics. The high hardness created by the low-temperature quenching leads to a planetary gear bolt previously produced in a cost-effective material, for example a steel alloy, mechanical strength which can not be found. This strength enables the bolts to withstand higher surface contact pressures than conventional bolts (e.g., contact pressures greater than 5000 MPa). In this way, a set of Planetenradbolzen be made with smaller planetary pins for installation in smaller operating installation spaces. Furthermore, the bolts can be used in other situations where deformation of the bolts due to high contact pressure is a problem.

An associated method for producing a Planetenradbolzensatzes is also disclosed. The method may include hardening the planetary gear bolt according to any one of methods 300 or 400 described above. A bearing unit with rollers and a gear hub with gear teeth are then attached to the Planetenradbolzen. In addition, opposite ends of the pinion gear are fixed to a carrier. In some implementations (i.e., when the planetary pin is hardened by method 400), securing the planetary pin to the carrier includes caulking in which the ends of the pinion gear are deformed. Further, in some embodiments, the method includes hardening a plurality of planetary pin bolts and securing each of the pinion pin bolts to a different location on the carrier.

After the foregoing detailed description of the currently preferred embodiments, it must be understood and obvious to those skilled in the art that numerous physical changes, of which only some are exemplified in the foregoing detailed description, could be made without the inventive concepts embodied herein and change principles. It should also be understood that numerous embodiments incorporating only portions of the preferred embodiment are possible, and with respect to these parts, are not alteratory of the inventive concepts and principles of the invention embodied herein. For this reason, the present embodiment and optional embodiments of the invention are to be considered in all respects as illustrative and not restrictive, as the scope of the invention is indicated by the appended claims rather than the foregoing description, so that all alternative embodiments and changes made to the present embodiment, which are to be understood in the sense of the claims and are within the range of equivalence of the claims, thus covered by the claims.

LIST OF REFERENCE NUMBERS

10

Planetenradbolzensatz

12

carrier

14

planet

16

Wheel center

18

gear teeth

20

storage unit

22

bolt

24

Radial roller bearings

26

bearing cage

28

Outer surface

30

Middle section

32

end

34

end surfaces

36

Operating depth

38

section

40

Hardened section

42

Enriched section

Claims (10)

Method of hardening a planetary pin, including: Carbonitriding an outer peripheral surface of the planetary pin, Quenching the planetary pin in oil at a temperature between about 120 ° and 150 ° C, Quenching the Planetenradbolzens in a cryogenic liquid at a temperature between about -70 ° C and -120 ° C, and Starting the planet gear bolt, wherein after cranking, the outer peripheral surface of the planetary gear pin has a hardened portion having a surface hardness of HV 832 or more and wherein the material of the bolt retains a hardness of at least HV 513 to a depth of at least 0.5 mm , Method according to Claim 1 wherein, after quenching in oil, the cured portion has between 5% and 25% remaining austenite. Method according to Claim 2 wherein, after quenching in a cryogenic liquid, the cured portion has less than 5% remaining austenite. Method according to Claim 1 , further comprising: high temperature quenching of the planetary pin, and induction hardening of the surface of the pinion pin. Method according to Claim 4 wherein high temperature quenching and induction hardening are carried out after quenching in oil and before quenching in the cryogenic liquid. Method for producing a planetary gear set comprising: Hardening a planetary pin by: Carbonitriding an outer peripheral surface of the planetary pin, Quenching the planetary pin in oil at a temperature of between about 120 ° and 150 ° C, Quenching the planetary pin in a cryogenic liquid at a temperature of between about -70 ° and -120 ° C, and Starting the planetary pin, wherein after annealing, the outer peripheral surface of the planetary gear has a surface hardness of HV 832 or more, and the material of the bolt retains a hardness of at least HV 513 to a depth of at least 0.5 mm, Attaching a bearing unit with radial roller bearings and a gear teeth having a wheel body to the Planetenradbolzen, and Attaching opposite ends of the planetary pin to a carrier. Method according to Claim 6 further comprising high temperature quenching of the planetary gear pin and induction hardening of the surface of the planetary gear pin. Method according to Claim 7 wherein high temperature quenching and induction hardening are carried out after quenching in oil and before quenching in the cryogenic liquid. Method according to Claim 8 wherein, after tempering, end faces of the planetary gear bolt have a hardness of between HV 170 and HV 350. Method according to Claim 9 wherein attaching the opposite ends of the planetary pin to the carrier includes caulking the opposite ends.

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